Electrical flight controls have been in use for many years in aviation. In particular, in certain airplanes such as the Airbus A 320, pilot orders are transmitted from the cockpit to a computer which actuates electrically-controlled servo-valves. Each of the servo-valves controls a hydraulic circuit which actuates an actuator with the displacement thereof being mechanically connected to one of the flight control members to be moved (flap or control surface).
To ensure control safety and to avoid breakdown of an electrical circuit giving rise to a complete breakdown of the member whose position is under control, one solution consists in controlling the hydraulic circuit of the displacement actuator connected to said member via four electrical circuits that control four mechanical displacements. Mechanical means integrated in the hydraulic circuit enable motion to be transmitted to the actuator which is a mean of said four displacements.
In the event of failure in one of the control circuits, the other three control circuits maintain the position of the flight control member.
In theory, the apparatus can withstand three successive failures of the control circuits.
Nevertheless, that solution is mechanically very complex.